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<tr class="t-nv"><td colspan="5"> <a href="const_cast.html" title="cpp/language/const cast"><tt>const_cast</tt></a> - <a href="reinterpret_cast.html" title="cpp/language/reinterpret cast"><tt>reinterpret_cast</tt></a></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Memory allocation</td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="new.html" title="cpp/language/new"> <code>new</code> expression</a></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="delete.html" title="cpp/language/delete"> <code>delete</code> expression</a></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="this.html" title="cpp/language/this"> <code>this</code> pointer</a></td></tr>
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<tr class="t-nv-h2"><td colspan="5"> Class-specific function properties</td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="virtual.html" title="cpp/language/virtual"> Virtual function</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="override.html" title="cpp/language/override"> <code>override</code> specifier</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="final.html" title="cpp/language/final"> <code>final</code> specifier</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
</table></div></td><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="explicit.html" title="cpp/language/explicit"><tt>explicit</tt></a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="static.html" title="cpp/language/static"><tt>static</tt></a> </td></tr>
</table></div></td></tr>
<tr class="t-nv-h2"><td colspan="5"> Special member functions</td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="default_constructor.html" title="cpp/language/default constructor"> Default constructor</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="copy_constructor.html" title="cpp/language/copy constructor"> Copy constructor</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="move_constructor.html" title="cpp/language/move constructor"> Move constructor</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="as_operator.html" title="cpp/language/as operator" class="mw-redirect"> Copy assignment</a></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="move_operator.html" title="cpp/language/move operator" class="mw-redirect"> Move assignment</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
<tr class="t-nv"><td colspan="5"> <a href="destructor.html" title="cpp/language/destructor"> Destructor</a></td></tr>
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<tr class="t-nv-h1"><td colspan="5"><a href="templates.html" title="cpp/language/templates"> Templates</a> </td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="class_template.html" title="cpp/language/class template"> Class template </a></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="template_specialization.html" title="cpp/language/template specialization"> Template specialization</a></td></tr>   
<tr class="t-nv"><td colspan="5"> <a href="parameter_pack.html" title="cpp/language/parameter pack"> Parameter packs</a> <span class="t-mark-rev t-since-cxx11">(C++11)</span></td></tr>
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<tr class="t-nv-h1"><td colspan="5"> Miscellaneous </td></tr>
<tr class="t-nv-col-table"><td><div><table class="t-nv-begin" cellpadding="0" style="">
<tr class="t-nv"><td colspan="5"> <a href="asm.html" title="cpp/language/asm"> Inline assembly</a></td></tr>
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<tr class="t-nv"><td colspan="5"> <a href="history.html" title="cpp/language/history"> History of C++</a></td></tr>
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</div><div></div></div></div></div><div class="t-navbar-sep"> </div><div class="t-navbar-head"><a href="basic_concepts.html" title="cpp/language/basic concepts"> Basic Concepts</a><div class="t-navbar-menu"><div><div style="display:inline-block">
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<tr class="t-nv"><td colspan="5"> <a href="lookup.html" title="cpp/language/lookup"> Name lookup</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <strong class="selflink"> Qualified name lookup</strong> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="unqualified_lookup.html" title="cpp/language/unqualified lookup"> Unqualified name lookup</a> </td></tr>
<tr class="t-nv"><td colspan="5"> <a href="as_if.html" title="cpp/language/as if"> The as-if rule</a></td></tr>
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</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>A <i>qualified</i> name is a name that appears on the right hand side of the scope resolution operator <code><b>::</b></code> (see also <a href="name.html#Qualified_identifiers" title="cpp/language/identifiers">qualified identifiers</a>).
A qualified name may refer to a 
</p>
<ul><li> class member (including static and non-static functions, types, templates, etc)
</li><li> namespace member (including another namespace)
</li><li> enumerator
</li></ul>
<p>If there is nothing on the left hand side of the <code><b>::</b></code>, the lookup considers only declarations made in the global namespace scope (or introduced into the global namespace by a <a href="namespace.html" title="cpp/language/namespace">using declaration</a>). This makes it possible to refer to such names even if they were hidden by a local declaration:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw1">struct</span> std <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
 
    <a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"fail<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="co1">// Error: unqualified lookup for 'std' finds the struct</span>
    <span class="sy4">::</span><a href="../io/cout.html"><span class="kw1762">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">"ok<span class="es1">\n</span>"</span><span class="sy4">;</span> <span class="co1">// OK: ::std finds the namespace std</span>
<span class="br0">}</span></pre></div></div>
<p>Before name lookup can be performed for the name on the right hand side of <code><b>::</b></code>, lookup must be completed for the name on its left hand side (unless a <a href="decltype.html" title="cpp/language/decltype">decltype</a> expression is used, or there is nothing on the left). This lookup, which may be qualified or unqualified, depending on whether there's another <code><b>::</b></code> to the left of that name, considers only namespaces, class types, enumerations, and templates whose specializations are types. If the name found on the left does not designate a namespace or a class, enumeration, or dependent type, the program is ill-formed:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> A
<span class="br0">{</span>
    <span class="kw4">static</span> <span class="kw4">int</span> n<span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw4">int</span> A<span class="sy4">;</span>
    A<span class="sy4">::</span><span class="me2">n</span> <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span> <span class="co1">// OK: unqualified lookup of A to the left of :: ignores the variable</span>
    A b<span class="sy4">;</span>       <span class="co1">// Error: unqualified lookup of A finds the variable A</span>
<span class="br0">}</span>
 
<span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span>
<span class="kw1">struct</span> B <span class="sy4">:</span> A <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">namespace</span> N
<span class="br0">{</span>
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw4">int</span><span class="sy1">&gt;</span>
    <span class="kw4">void</span> B<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
 
    <span class="kw4">int</span> f<span class="br0">(</span><span class="br0">)</span>
    <span class="br0">{</span>
        <span class="kw1">return</span> B<span class="sy1">&lt;</span><span class="nu0">0</span><span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">n</span><span class="sy4">;</span> <span class="co1">// error: N::B&lt;0&gt; is not a type</span>
    <span class="br0">}</span>
<span class="br0">}</span></pre></div></div>
<p>When a qualified name is used as a <a href="declarations.html" title="cpp/language/declarations">declarator</a>, then <a href="unqualified_lookup.html" title="cpp/language/unqualified lookup">unqualified lookup</a> of the names used in the same declarator that follow that qualified name, but not the names that precede it, is performed in the scope of the member's class or namespace:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">class</span> X <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">constexpr</span> <span class="kw4">int</span> number <span class="sy1">=</span> <span class="nu0">100</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> C
<span class="br0">{</span>
    <span class="kw1">class</span> X <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
    <span class="kw4">static</span> <span class="kw4">const</span> <span class="kw4">int</span> number <span class="sy1">=</span> <span class="nu0">50</span><span class="sy4">;</span>
    <span class="kw4">static</span> X arr<span class="br0">[</span>number<span class="br0">]</span><span class="sy4">;</span>
<span class="br0">}</span><span class="sy4">;</span>
 
X C<span class="sy4">::</span><span class="me2">arr</span><span class="br0">[</span>number<span class="br0">]</span>, brr<span class="br0">[</span>number<span class="br0">]</span><span class="sy4">;</span>    <span class="co1">// Error: look up for X finds ::X, not C::X</span>
C<span class="sy4">::</span><span class="me2">X</span> C<span class="sy4">::</span><span class="me2">arr</span><span class="br0">[</span>number<span class="br0">]</span>, brr<span class="br0">[</span>number<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// OK: size of arr is 50, size of brr is 100</span></pre></div></div>
<p>If <code><b>::</b></code> is followed by the character <code><b>~</b></code> that is in turn followed by an identifier (that is, it specifies a destructor or pseudo-destructor), that identifier is looked up in the same scope as the name on the left hand side of <code><b>::</b></code>
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> C <span class="br0">{</span> <span class="kw1">typedef</span> <span class="kw4">int</span> I<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">typedef</span> <span class="kw4">int</span> I1, I2<span class="sy4">;</span>
 
<span class="kw4">extern</span> <span class="kw4">int</span> <span class="sy2">*</span>p, <span class="sy2">*</span>q<span class="sy4">;</span>
 
<span class="kw1">struct</span> A <span class="br0">{</span> ~A<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">typedef</span> A AB<span class="sy4">;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    p<span class="sy2">-</span><span class="sy1">&gt;</span>C<span class="sy4">::</span><span class="me2">I</span><span class="sy4">::</span>~I<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// the name I after ~ is looked up in the same scope as I before ::</span>
                   <span class="co1">// (that is, within the scope of C, so it finds C::I)</span>
 
    q<span class="sy2">-</span><span class="sy1">&gt;</span>I1<span class="sy4">::</span>~I2<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>  <span class="co1">// The name I2 is looked up in the same scope as I1</span>
                   <span class="co1">// that is, from the current scope, so it finds ::I2</span>
 
    AB x<span class="sy4">;</span>
    x.<span class="me1">AB</span><span class="sy4">::</span>~AB<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>   <span class="co1">// The name AB after ~ is looked up in the same scope as AB before ::</span>
                   <span class="co1">// that is, from the current scope, so it finds ::AB</span>
<span class="br0">}</span></pre></div></div>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<h4> <span class="mw-headline" id="Enumerators">Enumerators</span></h4>
<p>If the lookup of the left-hand side name comes up with an <a href="enum_class.html" title="cpp/language/enum">enumeration</a> (either scoped or unscoped), the lookup of the right-hand side must result in an enumerator that belongs that enumeration, otherwise the program is ill-formed.
</p>
</td>
<td><span class="t-mark-rev t-since-cxx11">(since C++11)</span></td></tr>
</table>
<h4><span class="mw-headline" id="Class_members">Class members</span></h4>
<p>If the lookup of the left hand side name comes up with a class/struct or union name, the name on the right hand side of <code><b>::</b></code> is looked up in the scope of that class (and so may find a declaration of a member of that class or of its base), with the following exceptions
</p>
<ul><li> A destructor is looked up as described above (in the scope of the name to the left of ::)
</li><li> A conversion-type-id in a <a href="cast_operator.html" title="cpp/language/cast operator">user-defined conversion</a> function name is first looked up in the scope of the class. If not found, the name is then looked up in the current scope. 
</li><li> names used in template arguments are looked up in the current scope (not in the scope of the template name)
</li><li> names in <a href="namespace.html" title="cpp/language/namespace">using-declarations</a> also consider class/enum names that are hidden by the name of a variable, data member, function, or enumerator declared in the same scope
</li></ul>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: micro-examples for the above </td></tr></table>
<p>If the right hand side of <code><b>::</b></code> names the same class as the left hand side, the name designates the <a href="initializer_list.html" title="cpp/language/constructor">constructor</a> of that class. Such qualified name can only be used in a declaration of a constructor and in the <a href="using_declaration.html" title="cpp/language/using declaration">using-declaration</a> for an <a href="using_declaration.html#Inheriting_constructors" title="cpp/language/using declaration">inheriting constructor</a>. In those lookups where function names are ignored (that is, when looking up a name on the left of <code><b>::</b></code>, when looking up a name in <a href="elaborated_type_specifier.html" title="cpp/language/elaborated type specifier">elaborated type specifier</a>, or <a href="derived_class.html" title="cpp/language/derived class">base specifier</a>), the same syntax resolves to the injected-class-name:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> A <span class="br0">{</span> A<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> B <span class="sy4">:</span> A <span class="br0">{</span> B<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
A<span class="sy4">::</span><span class="me2">A</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// A::A names a constructor, used in a declaration</span>
B<span class="sy4">::</span><span class="me2">B</span><span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span><span class="br0">}</span> <span class="co1">// B::B names a constructor, used in a declaration</span>
 
B<span class="sy4">::</span><span class="me2">A</span> ba<span class="sy4">;</span>  <span class="co1">// B::A names the type A (looked up in the scope of B)</span>
A<span class="sy4">::</span><span class="me2">A</span> a<span class="sy4">;</span>   <span class="co1">// Error, A::A does not name a type</span>
 
<span class="kw1">struct</span> A<span class="sy4">::</span><span class="me2">A</span> a2<span class="sy4">;</span> <span class="co1">// OK: lookup in elaborated type specifier ignores functions</span>
                <span class="co1">// so A::A simply names the class A as seen from within the scope of A</span>
                <span class="co1">// (that is, the injected-class-name)</span></pre></div></div>
<p>Qualified name lookup can be used to access a class member that is hidden by a nested declaration or by a derived class. A call to a qualified member function is never virtual
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">struct</span> B <span class="br0">{</span> <span class="kw1">virtual</span> <span class="kw4">void</span> foo<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw1">struct</span> D <span class="sy4">:</span> B <span class="br0">{</span> <span class="kw4">void</span> foo<span class="br0">(</span><span class="br0">)</span> override<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    D x<span class="sy4">;</span>
    B<span class="sy3">&amp;</span> b <span class="sy1">=</span> x<span class="sy4">;</span>
 
    b.<span class="me1">foo</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>    <span class="co1">// calls D::foo (virtual dispatch)</span>
    b.<span class="me1">B</span><span class="sy4">::</span><span class="me2">foo</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// calls B::foo (static dispatch)</span>
<span class="br0">}</span></pre></div></div>
<h4><span class="mw-headline" id="Namespace_members">Namespace members</span></h4>
<p>If the name on the left of <code><b>::</b></code> refers to a namespace or if there is nothing on the left of <code><b>::</b></code> (in which case it refers to the global namespace), the name that appears on the right hand side of <code><b>::</b></code> is looked up in the scope of that namespace, except that 
</p>
<ul><li> names used in template arguments are looked up in the current scope
</li></ul>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">namespace</span> N
<span class="br0">{</span>
    <span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">typename</span> T<span class="sy1">&gt;</span>
    <span class="kw1">struct</span> foo <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
 
    <span class="kw1">struct</span> X <span class="br0">{</span><span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span>
 
N<span class="sy4">::</span><span class="me2">foo</span><span class="sy1">&lt;</span>X<span class="sy1">&gt;</span> x<span class="sy4">;</span> <span class="co1">// error: X is looked up as ::X, not as N::X</span></pre></div></div>
<p>Qualified lookup within the scope of a <a href="namespace.html" title="cpp/language/namespace">namespace</a> <code>N</code> first considers all declarations that are located in <code>N</code> and all declarations that are located in the <a href="namespace.html#Inline_namespaces" title="cpp/language/namespace">inline namespace members</a> of <code>N</code> (and, transitively, in their inline namespace members). If there are no declarations in that set then it considers declarations in all namespaces named by <a href="namespace.html#Using-directives" title="cpp/language/namespace">using-directives</a> found in <code>N</code> and in all transitive inline namespace members of <code>N</code>. The rules are applied recursively:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw4">int</span> x<span class="sy4">;</span>
 
<span class="kw1">namespace</span> Y
<span class="br0">{</span>
    <span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">float</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw4">void</span> h<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw1">namespace</span> Z
<span class="br0">{</span>
    <span class="kw4">void</span> h<span class="br0">(</span><span class="kw4">double</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw1">namespace</span> A
<span class="br0">{</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> Y<span class="sy4">;</span>
    <span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw4">void</span> g<span class="br0">(</span><span class="kw4">int</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw4">int</span> i<span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw1">namespace</span> B
<span class="br0">{</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> Z<span class="sy4">;</span>
    <span class="kw4">void</span> f<span class="br0">(</span><span class="kw4">char</span><span class="br0">)</span><span class="sy4">;</span>
    <span class="kw4">int</span> i<span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw1">namespace</span> AB
<span class="br0">{</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> A<span class="sy4">;</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> B<span class="sy4">;</span>
    <span class="kw4">void</span> g<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> h<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    AB<span class="sy4">::</span><span class="me2">g</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>  <span class="co1">// AB is searched, AB::g found by lookup and is chosen AB::g(void)</span>
              <span class="co1">// (A and B are not searched)</span>
 
    AB<span class="sy4">::</span><span class="me2">f</span><span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// First, AB is searched, there is no f</span>
              <span class="co1">// Then, A, B are searched</span>
              <span class="co1">// A::f, B::f found by lookup</span>
              <span class="co1">// (but Y is not searched so Y::f is not considered)</span>
              <span class="co1">// overload resolution picks A::f(int)</span>
 
    AB<span class="sy4">::</span><span class="me2">x</span><span class="sy2">++</span><span class="sy4">;</span>  <span class="co1">// First, AB is searched, there is no x</span>
              <span class="co1">// Then A, B are searched. There is no x</span>
              <span class="co1">// Then Y and Z are searched. There is still no x: this is an error</span>
 
    AB<span class="sy4">::</span><span class="me2">i</span><span class="sy2">++</span><span class="sy4">;</span>  <span class="co1">// AB is searched, there is no i</span>
              <span class="co1">// Then A, B are searched. A::i and B::i found by lookup: this is an error</span>
 
    AB<span class="sy4">::</span><span class="me2">h</span><span class="br0">(</span><span class="nu16">16.8</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// First, AB is searched: there is no h</span>
                 <span class="co1">// Then A, B are searched. There is no h</span>
                 <span class="co1">// Then Y and Z are searched.</span>
                 <span class="co1">// lookup finds Y::h and Z::h. Overload resolution picks Z::h(double)</span>
<span class="br0">}</span></pre></div></div>
<p>It is allowed for the same declaration to be found more than once:
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="kw1">namespace</span> A <span class="br0">{</span> <span class="kw4">int</span> a<span class="sy4">;</span> <span class="br0">}</span>
 
<span class="kw1">namespace</span> B <span class="br0">{</span> <span class="kw1">using</span> <span class="kw1">namespace</span> A<span class="sy4">;</span> <span class="br0">}</span>
 
<span class="kw1">namespace</span> D <span class="br0">{</span> <span class="kw1">using</span> A<span class="sy4">::</span><span class="me2">a</span><span class="sy4">;</span> <span class="br0">}</span>
 
<span class="kw1">namespace</span> BD
<span class="br0">{</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> B<span class="sy4">;</span>
    <span class="kw1">using</span> <span class="kw1">namespace</span> D<span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> g<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    BD<span class="sy4">::</span><span class="me2">a</span><span class="sy2">++</span><span class="sy4">;</span> <span class="co1">// OK: finds the same A::a through B and through D</span>
<span class="br0">}</span></pre></div></div>
<table class="metadata plainlinks ambox mbox-small-left ambox-notice" style=""><tr><td class="mbox-empty-cell"></td><td class="mbox-text" style="">This section is incomplete<br>Reason: the rest of N4861 6.5.3.2[namespace.qual], try to shorten their examples </td></tr></table>
<h3><span class="mw-headline" id="Defect_reports">Defect reports</span></h3>
<p>The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
</p>
<table class="dsctable" style="font-size:0.8em">
<tr>
<th> DR
</th>
<th> Applied to
</th>
<th> Behavior as published
</th>
<th> Correct behavior
</th></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="https://cplusplus.github.io/CWG/issues/215.html">CWG 215</a>
</td>
<td> C++98
</td>
<td> the name preceding <code><b>::</b></code> must be a class name or namespace<br>name, so template parameters were not allowed there
</td>
<td> the name must designate a class,<br>namespace or dependent type
</td></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="https://cplusplus.github.io/CWG/issues/318.html">CWG 318</a>
</td>
<td> C++98
</td>
<td> if the right hand side of <code><b>::</b></code> names the same class<br>as the left hand side, the qualified name was always<br>considered to name the constructor of that class
</td>
<td> only name the constructor<br>when acceptable (e.g. not in<br>an elaborated type specifier)
</td></tr></table>
<h3><span class="mw-headline" id="See_also">See also</span></h3>
<ul><li> <a href="unqualified_lookup.html" title="cpp/language/unqualified lookup">Unqualified name lookup</a> 
</li><li> <a href="scope.html" title="cpp/language/scope">Scope</a> 
</li><li> <a href="adl.html" title="cpp/language/adl">Argument-dependent lookup</a> 
</li><li> <a href="function_template.html" title="cpp/language/function template">Template argument deduction</a>
</li><li> <a href="overload_resolution.html" title="cpp/language/overload resolution">Overload resolution</a>
</li></ul>

<!-- 
NewPP limit report
Preprocessor visited node count: 3174/1000000
Preprocessor generated node count: 9357/1000000
Post‐expand include size: 129142/2097152 bytes
Template argument size: 17910/2097152 bytes
Highest expansion depth: 17/40
Expensive parser function count: 0/100
-->

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